...or just don't let them explode!
Seriously, smoke powder is not that easy to come by, barrels of that stuff just shouldn't be "everywhere".
Oh I agree, if they want to keep the exploding barrels, that should be very rare for a few encounters, to make them special. I could see something like an encounter in an alchemists lab where there was a few barrels.
With these exploding Barrels, why have they not completely changed warfare? Image a Trebuchet with them? Naval combat would be totally changed, these barrels put Greek Fire to shame.
